First, a general construction of a scroll compressor 1A of a closed vertical type in which a refrigerant compressing section is arranged above an electric motor will be described with reference to FIG. 4. For this scroll compressor 1A, the interior of a closed shell 2 is divided into a compression chamber CC having a refrigerant compressing section 4 and an electric motor chamber MC having an electric motor 5 by a main frame 3.
A rotational driving force generated by the electric motor 5 is transmitted to the refrigerant compressing section 4 via a rotational drive shaft 6, and revolves an orbiting scroll 42, which is fixed to the tip end of the rotating drive shaft 6, with respect to a fixed scroll 41, by which a refrigerant is compressed.
Usually, the rotational drive shaft 6 includes a main shaft 61 disposed coaxially in the electric motor chamber MC, a crank shaft 62 fixed integrally to one end (upper end in FIG. 4) of the main shaft 61, and a subsidiary shaft 66 fixed integrally to the other end of the main shaft 61.
The crank shaft 62 is arranged so as to be eccentric by a predetermined distance with respect to the main shaft 61 to revolve the orbiting scroll 42 of the refrigerant compressing section 4. The subsidiary shaft 66 is fixed coaxially with the main shaft 61.
The main shaft 61 is supported by a main bearing 31 of the main frame 3, and the subsidiary shaft 66 at the other end (lower end of FIG. 4) of the main shaft 61 is supported by a subsidiary bearing 71 of a sub-frame 7.
In the scroll compressor, the crank shaft 62 is broadly divided into two types as described below. Firstly, a first type (hereinafter referred to as type 1) is a type in which as shown in FIG. 4, the crank shaft diameter Dc is smaller than the main shaft diameter Dm, and the crank shaft 62 is arranged within the outside diameter of the main shaft 61 when viewed in the axial direction. Specifically, in type 1, the eccentricity e of the crank shaft 62 has a relation of e≦(Dm−Dc)/2.
According to type 1, when the compressor is assembled, the rotational drive shaft 6 can be inserted from either the compression chamber CC side or the electric motor chamber MC side with respect to the main bearing 31 of the main frame 3. However, this rotational drive shaft 6 has no portion for supporting its weight. Therefore, usually, after the refrigerant compressing section 4 consisting of the fixed scroll 41 and the orbiting scroll 42 has been assembled to the main frame 3, the rotational drive shaft 6 is inserted into the orbiting scroll 42 from the electric motor chamber MC side.
Secondly, a second type is a type in which for example, as shown in FIG. 5, the main shaft diameter Dm is approximately equal to the crank shaft diameter Dc, and the crank shaft 62 is shifted by eccentricity e from the main shaft 61. Specifically, in the second type, the eccentricity e has a relation of e>(Dm−Dc)/2. This second type is further classified into two subclasses.
First, a first subclass (hereinafter referred to as type 2-1) is a type in which, for example, as described in Japanese Patent No. 2572215, a main bearing of a main frame is formed of a roller bearing, and a hook-shaped “relief” is provided between the crank shaft and the main shaft, and this “relief” is slid in a radial direction in a main shaft receiving portion so that the crank shaft can be inserted from the electric motor chamber MC side. According to this type, without decreasing the crank shaft diameter, the crank shaft can be inserted from the electric motor chamber MC side as in the above-described type 1.
Next, a scroll compressor 1B of a second subclass (hereinafter referred to as type 2-2) is of a type in which as shown in FIG. 5, a flange portion 63 that has a larger diameter than the main shaft 61 and is coaxial with the main shaft 61 is provided between the main shaft 61 and the crank shaft 62 to support the weight of the rotational drive shaft 6. In this case, it is necessary to insert the rotational drive shaft 6 into the main frame 3 before the refrigerant compressing section 4 is assembled to the main frame 3. After the refrigerant compressing section 4 has been assembled, the rotational drive shaft 6 does not come off from the main frame 3 even if the compressor is moved vertically during the assembly of the whole of the compressor.
However, the above-described scroll compressors 1A and 1B have problems as described below. In type 1, in order to give revolving motion necessary for compression of refrigerant to the orbiting scroll 42, it is necessary to make design so that the crank shaft diameter Dc is about 30% smaller than the main shaft diameter Dm. The small diameter of the crank shaft 62 inevitably decreases the load-carrying strength, so that there is a fear of decreased reliability in terms of strength.
When an attempt is made to increase the crank shaft diameter Dc to enhance the reliability, the main shaft diameter Dm must be increased relatively greater than necessary for the load-carrying strength. Accordingly, there arises a problem of increased sliding friction loss of main shaft.
Referring to FIG. 4, when a load applied to a bearing portion 421 of the crank shaft 62 against compressed gas is taken as Fc, the axial distance from the crank shaft 62 to the main bearing 31 of the main frame 3 is taken as Lm, and the axial distance from the crank shaft 62 to the subsidiary bearing 71 is taken as Ls, the load Fm applied to the main shaft 31 is expressed asFm=Fc×(Ls/(Ls−Lm))From this formula, it can be seen that as Lm decreases, the load Fm applied to the main bearing 31 decreases.
Contrarily, in type 2-1, the axial distance between the main bearing 31 and the crank bearing 421 is inevitably long, so that the load applied to the main bearing 31 increases. Therefore, it is difficult to support the main bearing 31 by a sliding bearing, and thus the main bearing 31 must be changed to a roller bearing. However, the roller bearing is more expensive than the sliding bearing.
In type 2-2, the axial distance Lm can be shortened as compared with type 2-1. However, since the flange portion 63 is provided between the main shaft 61 and the crank shaft 62, the axial distance between the main bearing 31 and the crank bearing 421 inevitably increases by the thickness (axial length) of the flange portion 63. Therefore, the load applied to the main bearing 31 is still high, which presents a problem in that the sliding friction loss increases resultantly.